A fastening portion structure for a vehicle is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2008-215465. In this fastening portion structure for a vehicle, a vehicle body skeleton member that is formed from a composite material of fibers and resin is fastened to a fastened-to member via a stepped washer made of metal. The stepped washer has a boss portion that is shaped as a short cylinder, and, at one axial direction end side of this boss portion, a flange portion having an enlarged diameter. The boss portion is inserted into a counterbored hole that is formed in the vehicle body skeleton member. The region between the boss portion and the flange portion, and the vehicle body skeleton member, is adhered via an adhesive.
On the other hand, a part fastening structure for a vehicle is disclosed in JP-A No. 2009-204159. In this part fastening structure for a vehicle, a flanged collar nut made of metal is used in the fastening of a fastened-to member and a vehicle body skeleton member that is made of FRP. The flanged collar nut has a collar portion that passes through a through-hole of the vehicle body skeleton member, and a flange portion that projects out from one end side of this collar portion. The collar portion is press-fit into the through-hole. An adhesive is provided between the flange portion and the vehicle body skeleton member. The flanged collar nut is thereby mounted to the vehicle body skeleton member.